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Secondary welding of submarine pumice-lithic breccia at Mount Chalmers, Queensland, Australia

journal contribution
posted on 2023-05-16, 10:24 authored by Jocelyn McPhieJocelyn McPhie, Hunns, SR
Very thick units of massive pumice and lithic clast-rich breccia in the Early Permian Berserker beds at Mount Chalmers, Queensland, are deposits from cold, water-supported, volcaniclastic mass flows emplaced in a below-wave base submarine setting. Adjacent to syn-volcanic andesitic and rhyolitic sills and dykes, the pumice-lithic breccia shows a well-developed eutaxitic texture. The eutaxitic foliation is parallel to intrusive contacts and extends as far as a few metres away from the contact. At these sites, pumice clasts are strongly flattened and tube vesicles within the pumice clasts are compacted and aligned parallel to the direction of flattening. Some lenticular pumice clasts contain small (≤2 mm), round, quartz-filled amygdales and spherulites. Further away from the sills and dykes, the pumice clasts have randomly oriented, delicate tube vesicle structure and are blocky or lensoid in shape. Round amygdales were generated by re-vesiculation of the glass and the spherulites indicate devitrification of the glass at relatively high temperatures. The eutaxitic texture is therefore attributed to re-heating and welding compaction of glassy pumice-lithic breccia close to contacts with intrusions. In cases involving sills, secondary welding along the contacts formed extensive, conformable, eutaxitic zones in the pumice-lithic breccia that could be mistaken for primary welding compaction in a hot, primary pyroclastic deposit. © 1995 Springer-Verlag.

History

Publication title

Bulletin of Volcanology

Volume

57

Pagination

170-178

ISSN

0258-8900

Department/School

School of Natural Sciences

Publisher

Springer-Verlag

Place of publication

Berlin, Germany

Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the earth sciences

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